Technical Field
The invention relates to a process system for separating chemicals, a distillation column arrangement, and a method of separating chemicals.
Related Art
Distillation is a method commonly used in industry for separating substances dissolved in one another, based on different volatilities of the substances in a mixture. Distillation enables liquid substances dissolved in one another, as well as non-volatile and volatile substances to be separated.
Heteroazeotropic extractive distillation is an embodiment of distillation. A heteroazeotropic extractive distillation is described in Finnish Patent Publication FI 117633 B. In the method in question, a distillation step comprises utilizing the partial insolubility of water and furfural in one another, pressure dependence of azeotropes, extraction capacity of furfural as well as the binary azeotrope formed by furfural and water. In an azeotropic extraction method, the separation is implemented by a combination of azeotropic distillation and conventional extractive distillation. The method uses furfural simultaneously as both an extractant and an azeotrope forming agent for separating water from organic acids. Depending on the temperature, with water furfural forms either a homogeneous or heterogeneous azeotrope. In a temperature below 120° C., the azeotrope is heterogeneous, and therefore in a pressure range corresponding to this, extending from underpressure to moderate overpressure, the method is called heteroazeotropic extractive distillation. In the heteroazeotropic extractive distillation, the extractant has a double effect and generates two liquid phases, which enables the separation of water.
The safety classification for furfural used in the known solution has deteriorated in a REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) assessment. Further, when using an extractant, it is extremely important to control the mutual chemical reactions of the substances used in a process. At the same time, a need exists to separate chemicals in connection with an azeotropic extractive process, which is challenging as well.